Great idea OP! I love things like this that could open up multiple possibilities stemming from one single change. It could even be a piece of furniture in the house enabling it that costs "stuff" to include crafters or hell, I'd even pay crowns!
Besides group combat and conventional team duels, this would open up possibilities for mini games and fun guild contests and activities.
I don't know how difficult to implement this would be, but think of all the PvPer crown sales you would get if housing could also be a dojo!
The best type of content is the type that allows for more player-driven content to stem off of it. Other PvP games typically have a lot of success with similar features where players can build custom maps and gamemodes, etc, to the point where some people purely play just for the custom games.
It’s something that would require minimal effort from ZOS, yet would help eliminate a lot of the issues people currently have with PvP, since it gives people the tools to play how they want.